The invention relates to an anti-interference filter and lightning arrester device in a coaxial line for the transmission of high-frequency signals, comprising a housing with two connectors, the housing forming an outer conductor connected to ground, an inner conductor carried through the housing, a connection between inner conductor and housing for diverting overvoltages and a gas capsule diverter in the connection between inner conductor and housing.
Anti-interference filter and lightning arrester devices of this type are known. They serve for the purpose of protecting structural groupings, apparatus or facilities connected to lines, for example coaxial lines of telecommunication devices, against electromagnetic pulses (EMP), overvoltages and/or lightning currents. Electromagnetic pulses of artificial type can be generated for example by motors, switches, clocked power supplies or also in connection with nuclear events. Pulses of natural origin can result, for example, as a consequence of direct or indirect lightning strikes. The known protective circuits are disposed at the input side of the structural groupings, apparatus or facilities and/or are installed as a structural component in the coaxial line.
An EMP diverter of this type with a gas capsule or gas discharge overvoltage diverter is known from CH 660 261 A5. This EMP diverter comprises a housing serving as outer conductor and connected to ground. Disposed at both ends of the housing are connectors, by means of which the housing can be connected with one end each of a coaxial cable. Through the center of the housing is carried an inner conductor which, in the proximity of the connectors, can also be connected with the coaxial cable. Radially with respect to the inner conductor is disposed a housing portion, which serves for accommodating the overvoltage diverter in the form of a gas capsule. This overvoltage diverter is connected, on the one hand, to the inner conductor and, on the other hand, to the housing and therewith to ground. Gas capsule overvoltage diverters have the property that during normal operation their resistance is on the order of a few GΩ. Upon reaching a specified ignition voltage, an electric flashover occurs and the resistance of the gas capsule jumps to values of less than 1Ω. This state occurs in the case of interference if, for example, on the antenna side, an overvoltage occurs due to a lightning strike. The gas capsule overvoltage diverter protects the elements located on the apparatus side by diverting the overvoltage low-ohmically to ground. After the decay of the overvoltage, the gas capsule becomes high-ohmic and returns to the normal operating state, i.e. it acts again as an isolation. During the time interval in which the gas capsule is low-ohmic, the so-called arc burning voltage is connected to the gas capsule. This burning voltage is on the order of a few 10 V. As long as a current of a few 10 mA flows, the arc discharge persists and the gas capsule remains in the low-ohmic state. This may occur for example if across the coaxial cable or the anti-interference filter and lightning arrester device an additional DC control current is conducted or in the presence of high-frequency signals of relatively high power. In these cases a device with a gas capsule diverter has the considerable disadvantage that after a response, for example due to a lightning strike, it is no longer extinguished but rather remains permanently in the low-ohmic state. To restore the normal state, the DC control current must in this case be switched off and/or the high-frequency signal must be interrupted. Normally this requires switching off the particular facility and switching it on again, which entails considerable complications and/or is especially undesirable in communication facilities.